1. Field of the Invention
The present invention relates to a mammographic apparatus of capturing radiation image information of a breast, and a breast compression plate for compressing a breast and a breast fixing method for fixing a breast when an image of the breast is captured by the mammographic apparatus.
2. Description of the Related Art
In the medical field, there have widely been used radiation image capturing apparatus for applying a radiation emitted from a radiation source to a subject, and guiding the radiation that has passed through the subject to a solid-state detector or a stimulable phosphor panel, thereby recording radiation image information of the subject.
The solid-state detector includes a solid-state detecting unit which comprises a matrix of charge collecting electrodes formed on an insulating substrate and a radiation conductor disposed on the charge collecting electrodes for generating electric charges depending on the radiation that is applied to the radiation conductor. The electric charges generated by the radiation conductor and representing radiation image information are collected by the charge collecting electrodes and temporarily stored in an electric storage unit. The collected electric charges are converted into an electric signal, which is output from the solid-state detector.
The stimulable phosphor panel is a panel coated with a stimulable phosphor which, when exposed to an applied radiation, stores part of the energy of the radiation, and, when subsequently exposed to applied stimulating light such as laser beam or the like, emits light in proportion to the stored energy of the radiation. The radiation image information can be read from the stimulable phosphor panel by photoelectrically converting stimulated light that is emitted from the stimulable phosphor panel.
One of the radiation image capturing apparatus is known as a mammographic apparatus for use in breast cancer screening. The mammographic apparatus comprises an image capturing base for supporting a breast of a subject, the image capturing base incorporating a panel-shaped solid-state detector, a breast compression plate disposed opposite the image capturing base for pressing the breast against the image capturing base, and a radiation source for applying a radiation through the breast compression plate to the breast.
For capturing appropriate radiation image information of the breast, it is necessary to place the region to be imaged of the breast, which ranges from the chest wall of the subject to the nipple of the breast, properly in a predetermined range on the image capturing base.
U.S. Pat. No. 6,577,703 discloses an X-ray mammography apparatus wherein a breast compression plate is swingably supported by a rubber bushing, so that the breast compression plate follows the shape of a breast when the breast compression plate compresses the breast.
U.S. Pat. No. 5,706,327 discloses a mammographic compression apparatus wherein a breast compression plate is angularly movable about an axis substantially parallel to the chest wall of a subject. After the breast is compressed to a certain degree by the breast compression plate, a nipple end of the breast compression plate is angularly moved downwardly about the axis to compress the breast, particularly the mammary gland thereof.
U.S. Pat. Nos. 5,050,197 and 5,029,193 disclose mammographic apparatus wherein a breast compression plate has a chest end inclined downwardly. After a portion of a breast near the chest is compressed by the chest end of the breast compression plate, a nipple end of the breast compression plate is displaced toward an image capturing base to make the breast compression plate substantially horizontal.
According to U.S. Pat. Nos. 6,577,703 and 5,706,327, however, when the operator presses the breast compression plate against the breast while holding and positioning the breast with a hand, the breast compression plate is held against a wide area of the breast by following the shape of the breast. Therefore, after having pressed the breast compression plate against the breast, the operator finds it difficult to remove the hand, and may cause the breast to be displaced in position when removing the hand.
According to U.S. Pat. Nos. 5,050,197 and 5,029,193, in an initial phase of the process of compressing the breast, the portion of the breast near the chest is compressed by the chest end of the breast compression plate, whereas the other portion of the breast is free at the nipple end of the breast compression plate. Accordingly, after the breast is positioned on the image capturing base, the operator finds it easy to remove the hand.
However, as the portion of the breast near the nipple is not held by the breast compression plate in the initial phase of the breast compressing process, the portion of the breast near the nipple may possibly be displaced in position in the image capturing session.
Mammographic apparatus are capable of capturing various images of a breast, including a cranio-caudal view (CC) taken from above, a medio-lateral view (ML) taken outwardly from the center of the chest, or a medio-lateral oblique view (MLO) taken from an oblique view.
When the image capturing base and the breast compression plate are set to position the breast for capturing a medio-lateral view or a medio-lateral oblique view thereof, since the portion of the breast near the nipple is not held by the breast compression plate in the initial phase of the breast compressing process, as shown in FIG. 17 of the accompanying drawings, the portion of the breast 3 near the nipple tends to droop by gravity with respect to the predetermined range 2 on the image capturing base 1. As a result, the breast 3 is not positioned in an appropriate image capturing position.
Even if the operator holds and positions the breast with a hand, since the operator has to remove the hand at the time the breast compression plate approaches the image capturing base, the breast is liable to be displaced in position at this time.